Originally Posted by discountinvestigator
The TERR switch takes out TAD and TCF (sorry, but I do not know what these are) only and leaves Modes 1 to 5 available.
TAD is the Terrain Awareness Display (EGPWS terrain map) and TCF is Terrain Clearance Floor (EGPWS computation / warning boundary). If these are off i.e Terr Off/Fault then the Enhanced functions of GPWS will not be available, but the old style / standard GPWS (modes 1-5) should work. Remember that the old GPWS does not give you the same standard of protection as EGPWS does – take care.
See: www/egpws.com - ‘Operation’ – ‘Pilots Guides’ for more info